On the one hand, methods of this type are used in motor vehicles for voice- controlled intercom operation, but they are also used for supporting voice-input controlled electronic or electric modules. In this case, the fundamental problem is that, depending on the operating state, corresponding background noise is present in the motor vehicle. This background noise masks the voice commands. One- and two-way intercom systems in motor vehicles are advantageous in large vehicles, minibusses, and the like. However, they can also be used in normal passenger cars. Suppressing background noise or filtering out the voice command is still very important in the use of voice-controlled input units for electric components in the vehicle.
A voice-recognition device for a motor vehicle is described, for example in European Patent No. 0 078 014, where sensors signal or feed into the amplifier system of the voice- recognition device, whether or not the engine is running and/or the vehicle is moving. This device guides a level control, by which it is attempted to isolate the voice command from the background noise.
German Patent No. 37 42 929 describes a system having two microphones, one of the microphones being disposed at the mouth of the operator, and another in proximity, which is, however, for picking up the structure-borne noise. Both microphone signals are triggered so, that structure-borne noise can be subtracted from the total noise.
German Published Patent Application No. 197 05 471 describes a voice-recognition system using transverse filtering. In this case, a frequency analysis is performed, which is only used for the purpose of recognizing speech commands. No ambient-noise compensation is performed.
Filtering is described in International Patent Publication No. WO 97/34290, in which periodic interference signals are filtered out by ascertaining their periods and canceling them out by interference, using a generator, so that the voice signal remains.
German Patent No. 41 06 405 describes a method in which noise is subtracted from the voice signal, a plurality of microphones being used.
The use of a multiple microphone array is known from described in German Published Patent Application No. 39 25 589. When using the array in the motor vehicle, one of the microphones is disposed in the engine compartment and another microphone is disposed in the passenger compartment. Both signals are then subtracted. A disadvantage in this case, is that only the engine noise i.e. the actual operational noise of the vehicle itself, is subtracted from the total signal in the passenger compartment. Specific ambient noises are not, however, considered. The lack of feedback suppression presents a special problem. Wherever microphones and loudspeakers are arranged in acoustically coupleable proximity, the acoustic signal decoupled at the loudspeaker is fed back into the microphone. This results in so-called feedback and a subsequent overload.
German Published Patent Application No. 39 25 589 also describes a method, in which a composite signal is formed. The composite signal includes a voice signal and an external noise signal. A detection of the external noise is performed separately. The external noise and voice signals are filtered and subtracted from the composite signal. The results is used to control the filter. This method, however, cannot effectively prevent the occurrence of an echo and/or feedback.
A similar method is known from DE 39 25 589 A1, where a composite signal made of a voice signal and an external signal is formed. The additional picking-up of external noise takes place separately. The external-noise and voice signals are lead over a filter and are subtracted from the composite signal. Then, the result of the comparison controls the filter. A method of this type cannot effectively prevent the
Therefore, it is an object of the present invention to provide a method and device for operating voice-controlled systems in motor vehicles so that instances of feedback and